Large Format newbie questions

I went to the monthly antique/flea fair here in my home town and bought a Speed Graphic 4X5 in a normal condition with some signs of wear, but apperantly in working order and with the lens with no fungus, scratches, etc. Even if the camera is not working fine, I can go to the fair next month and throw it at the seller .

First question is about the plain film holders, can I use it any one (from any brand) or I have to use only the ones from graflex?

Are the bellows real leather? If so can I use the same products for caring leather? What I have to look also to see if the camera is in order, besides the normal things?
Thank you!

Before you buy anything, just look at the back of your camera. Pull the groundglass back a little bit and on the side where you would slide in a holder, on the face toward the lens, there will either be a slot or a ridge. The slot is for a ridge on corresponding international holders. These are the common ones. The ridge would require the slotted graflex-specific holders. It will probably have the slot and take normal, common holders.